IPAC2012 - List of Authors (van Rienen, U.)

Paper	Title	Page
MOPPC062	Eigenmode Computation for Cavities with Perturbed Geometry Based on a Series Expansion of Unperturbed Eigenmodes	277
	K. Brackebusch, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: Work supported by Federal Ministry for Research and Education BMBF under contracts 05H09HR5 and 05K10HRC. The geometry of an accelerator cavity determines its eigenmodes and thereby its performance characteristics. Therefore, accelerating performance and wakefield characteristics may be improved by an intentional modification of the geometry. However, undesired geometry perturbations due to manufacturing tolerances and operational demands can likewise impair it. To analyze the effects of geometry variations on the eigenmodes, parameter studies are to be undertaken. Using common eigenmode solvers it usually is necessary to perform a full eigenmode computation for each variation step, even if the geometry is only slightly altered. Parameter studies for cavity perturbations thus tend to be computationally extensive and inefficient. In this paper, we present the fundamentals of an efficient eigenmode computation method for varying cavity geometries. Knowing a set of initial eigenmodes of an unperturbed geometry, the method allows expanding the eigenmodes of any geometry that is part of the unperturbed one as a series of the initial eigenmodes. Thereby the computation effort may be significantly reduced. The method is demonstrated by means of analytically evaluable cavity geometries.

MOPPC063	Computation of the 2D Transverse Wake Function of an Electron Cloud for Different Parameters	280
	A. Markoviḱ, G. Pöplau, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: Work supported by DFG under contract number RI 814/20-2. A PIC simulation of the interaction of a positive charged bunch with an e-cloud yields the wake kick from the electrons on the tail particles of the bunch. The wake is induced from a certain offset in the transverse position of the head parts of the bunch which perturb the electron distribution. Such a pre-computed wake functions of each offset part of the bunch are forming a matrix which could be used for investigating single bunch stability under several assumptions. In this paper we investigate the linear scalability of the kick with the offset value. Furthermore we investigate the wake values for different realistic electron densities. Another important parameter for realizing the single bunch stability simulation is the optimal number of bunch slices in longitudinal direction. Here we study the thickness of the slices in conjunction with the mobility of the electrons around the beam axis.

MOPPC064	Simulation of the Behavior of Ionized Residual Gas in the Field of Electrodes	283
	G. Pöplau, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany A. Meseck HZB, Berlin, Germany
	Funding: Work supported by BMBF under contract number 05K10HRC Light sources of the next generation such as ERLs require minimal beam losses as well as a stable beam position and emittance over the time. Instabilities caused by ionized residual gas have to be avoided. In this paper we present simulations of the behavior of ionized residual gas in the field of clearing electrodes and investigate e.g. clearing times. For these simulations we apply MOEVE PIC Tracking developed at Rostock University. We demonstrate numerical results with parameters planed for the ERL BERLinPro.

Paper

Title

Page

Eigenmode Computation for Cavities with Perturbed Geometry Based on a Series Expansion of Unperturbed Eigenmodes

277

K. Brackebusch, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: Work supported by Federal Ministry for Research and Education BMBF under contracts 05H09HR5 and 05K10HRC.
The geometry of an accelerator cavity determines its eigenmodes and thereby its performance characteristics. Therefore, accelerating performance and wakefield characteristics may be improved by an intentional modification of the geometry. However, undesired geometry perturbations due to manufacturing tolerances and operational demands can likewise impair it. To analyze the effects of geometry variations on the eigenmodes, parameter studies are to be undertaken. Using common eigenmode solvers it usually is necessary to perform a full eigenmode computation for each variation step, even if the geometry is only slightly altered. Parameter studies for cavity perturbations thus tend to be computationally extensive and inefficient. In this paper, we present the fundamentals of an efficient eigenmode computation method for varying cavity geometries. Knowing a set of initial eigenmodes of an unperturbed geometry, the method allows expanding the eigenmodes of any geometry that is part of the unperturbed one as a series of the initial eigenmodes. Thereby the computation effort may be significantly reduced. The method is demonstrated by means of analytically evaluable cavity geometries.

MOPPC063

Computation of the 2D Transverse Wake Function of an Electron Cloud for Different Parameters

280

A. Markoviḱ, G. Pöplau, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Funding: Work supported by DFG under contract number RI 814/20-2.
A PIC simulation of the interaction of a positive charged bunch with an e-cloud yields the wake kick from the electrons on the tail particles of the bunch. The wake is induced from a certain offset in the transverse position of the head parts of the bunch which perturb the electron distribution. Such a pre-computed wake functions of each offset part of the bunch are forming a matrix which could be used for investigating single bunch stability under several assumptions. In this paper we investigate the linear scalability of the kick with the offset value. Furthermore we investigate the wake values for different realistic electron densities. Another important parameter for realizing the single bunch stability simulation is the optimal number of bunch slices in longitudinal direction. Here we study the thickness of the slices in conjunction with the mobility of the electrons around the beam axis.

MOPPC064

Simulation of the Behavior of Ionized Residual Gas in the Field of Electrodes

283

G. Pöplau, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
A. Meseck
HZB, Berlin, Germany

Funding: Work supported by BMBF under contract number 05K10HRC
Light sources of the next generation such as ERLs require minimal beam losses as well as a stable beam position and emittance over the time. Instabilities caused by ionized residual gas have to be avoided. In this paper we present simulations of the behavior of ionized residual gas in the field of clearing electrodes and investigate e.g. clearing times. For these simulations we apply MOEVE PIC Tracking developed at Rostock University. We demonstrate numerical results with parameters planed for the ERL BERLinPro.